For me, I'd say Superman is all three, primarily the first. All other superheroes, as we know them, exist because of him. In-story, I'm fine with him being the first of his generation, but that's still a first. He's the strongest - but not because his power levels are above all others (they don't have to be), but because Superman is as smart as he is powerful, with a strong sense of self and what he can do. That combo makes him stronger than anyone. And who he is and how he does what he does (Sacred said it perfectly) is what makes him the most inspiring.
So in-story, I'd say "inspiring" with heavy doses of the other two. For me as a fan, I'd say "first" with heavy doses of the other two.
To a certain degree, they're very inter-connected, imo.